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Employee Benefit Plan - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Age
Defined Benefit Plan Disclosure [Line Items]  
Eligible age for employees for participating in the plan 21evok_MinimumAgeOfEmployeeToParticipateInDefinedBenefitPlan
Company's contributions to employee benefit plan $ 0us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Future  
Defined Benefit Plan Disclosure [Line Items]  
Company's contributions to employee benefit plan $ 20,000us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FutureMember